Visualizing thermotectonic and denudation histories using apatite fission track thermochronology

摘要

Thermochronology, the use of temperature-sensitive radiometric dating methods to reconstruct the time-temperature histories of rocks, has proved to be an important means of constraining a variety of geological processes. In general, different depths within the Earth's crust are characterized by different temperature regimes and processes. Within the upper crustal environment, temperature can often be used as a proxy for depth, so that reconstructed cooling histories may reveal a record of rock movement towards the surface. That portion of this process which involves temperature variations within the uppermost ~150-200 deg C of crustal depth has been the basis for the application of low temperature thermochronology to a range of interdisciplinary problems in the Earth Sciences. The last fifteen or so years have sparked widespread interest in this field and this proliferation has been driven in part by advances in analytical techniques, numerical modeling, and fundamental changes of perspectives on the significance of radioisotopic ages (e.g., IvIcDougall and Harrison 1999; Gleadow et al. 2002a; Farley 2002). One area of rapidly growing interest, which has provided unprecedented insights in this regard, has been the quantification in time and space of surface processes and shallow crustal tectonism using low temperature thermochronology, often combined with complementary techniques structural analysis, geomorphic, numerical modeling, and cosmogenic isotope studies (e.g., House et al. 1998; Ehlers and Farley 2003: Belton et al. 2004: Ehlers 2005).One of the best established and most sensitive low temperature thermochronology methods available for reconstructing such histories in the upper ~3-5 km of the continental crust, over time scales of millions to hundreds of millions of years, is apatite fission track (AFT) thermochronology which responds to temperatures of typically <110 + - 10 deg C.